Image-forming devices such as copiers, printers and facsimiles include known electrophotographic systems in which charging, exposure, development, transfer, etc., are carried out using electrophotographic photoreceptors.
Such photoreceptors are known to include several layers, generally including: a substrate, an undercoating layer, an intermediate layer, an optional charge blocking layer, a charge generating layer over an undercoating layer and/or a blocking layer, a charge transport layer and an optional protective overcoat layer. These layers can be in a variety of orders to make up a functional device, and sometimes multiple layers can be combined in a single or mixed layer.
In the charge transport layer and the optional protective overcoat layer, hole transport molecules may be dispersed in a polymer binder. The hole transport molecules provide hole or electron transport properties, while the electrically inactive polymer binder provides mechanical properties.
Imaging members are generally exposed to repetitive electrophotographic cycling, which subjects the exposed charge transport layer or protective overcoat layer thereof to mechanical abrasion, chemical attack and heat. This repetitive cycling leads to gradual deterioration in the mechanical and electrical characteristics of the exposed charge transport layer.
In light of this deterioration, one type of protective overcoat layer has been used to provide increased crack, abrasion and scratch resistance of the photoreceptor when the photoreceptor is in a belt configuration. The layer is generally made up of three main components: a polyol binder, a melamine-formaldehyde curing agent and a hole transport material such as N,N′-diphenyl-N,N′-bis(3-hydroxyphenyl)-[1,1′:4′1″-terphenyl]-4,4″-diamine.
The production of a number of N,N′-diaryl-N,N′-di(hydroxyaryl)-aryl-diamine compounds, such as N,N′-diphenyl-N,N′-bis(3-hydroxyphenyl)-[1,1′:4′1″-terphenyl]-4,4″-diamine that is useful as the hole transport material in electrophotographic photoreceptors, often involves synthesis of intermediate materials which are generally costly and/or time-consuming to produce, and some of which involve a multi-step process.
Certain N,N′-diaryl-N,N′-di(hydroxyaryl)-aryl-diamine compounds may be produced by reaction of a diarylamine with an aryliodide under traditional Ullmann conditions (copper catalyst, high temperature, long reaction time) or the so-called ligand-accelerated Ullmann reaction that uses lower reaction temperatures but is still limited to the use of aryliodides. Aryliodides tend to be very expensive reagents. Furthermore, both of these reactions usually require lengthy and costly purification processes. These drawbacks, while nominal in a laboratory scale, pose significant challenges in scaling up a reaction to commercial level.
Accordingly, improved processes providing safe, cost-effective, and efficient methods for N,N′-((hydroxyl)m-diaryl)-N,N′-((hydroxyl)n-diaryl)-aryl-diamine production are desired.